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AS7221

Optical Characteristics

Datasheet

• PUBLIC

DS000479

• v4-00 • 2019-Jun-28

│ 12

Optical Characteristics

The XYZ chromatic white/color sensor, part of the AS7221 Cognitive Light Engine (CLE), is a next-

generation digital color sensor device. The sensor contains an integrating analog-to-digital converter

with 16-bit resolution ADC, which integrates current from photodiodes. Upon completion of the

conversion cycle, the result is transferred to the corresponding data registers to drive internal tuning

algorithms. Transfers are double-buffered to ensure integrity of the data is maintained.

Standard observer tri- stimulus (XYZ) interference filters

are applied to the SLM’s optical channels as

part of the CMOS process. This unique process enables filter responses that mimic the human eye

and is extremely stable over both operating temperature and time. This in turn allows lifetime

correlated color temperature (CCT) calibration to be performed as part of the manufacturing process.

Calibration is accomplished using standard white LEDs at a variety of CCTs to deliver high accuracy

and typically eliminate the need for light-by-light calibration in most designs. Note that any change of

the precalibrated measurement conditions have an impact on the accuracy of the measurement

results. In such cases a design-level diffuser or color brightness calibration is recommended to

achieve highest accuracies. The AS7221 provides 2 calibration matrices, a factory calibration and a

second application specific matrix to optimize the measurement performance. The additional

calibration values will be set using the Smart Lighting Command Set directives ATNORMGAIN and

ATNORMINTT. These settings will be saved in the external flash and reloaded automatically by the

sensor firmware. See Section 10 for description of the complete Smart Lighting Command Set.

The AS7221 LGA package contains an internal aperture that provides a package field of view (PFOV)

of ± 20.5°. External optics can be used as needed to expand or reduce this built in PFOV.

Sensor data readout to the maximum count value range is limited by the ADC. The maximum count

range value of 65535 is only reached with an integration time tINT of approximately 177.92 ms. Below

that value, the FSR will be less than the maximum 16-bit/65536 count maximum as described in the

chart below.

Figure 7:

Overview Signal Resolution

Bit Resolution

tINT in ms

Maximum Counts

2.78

1024

5.56

2048

11.12

4096

22.24

8192

44.48

16384

88.96

32768

177.92

65536

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